REGENERATION OF JUNCTIONAL EPITHELIUM AND ITS INNERVATION IN ADULT-RATS - A STUDY USING IMMUNOCYTOCHEMISTRY FOR P75 NERVE GROWTH-FACTOR RECEPTOR AND CALCITONIN-GENE-RELATED PEPTIDE

Junctional epithelium (JE) is a rapidly proliferating tissue that conn ects the gum to the tooth, that provides a free surface for bidirectio nal movement of substances between the body and the oral cavity, and t hat participates in defense against bacterial infection. It is innerva ted by numerous sensory nerve fibers that are immunoreactive (IR) for neuropeptides such as calcitonin gene-related peptide (CGRP), and for low affinity nerve growth factor receptor (p75-NGFR). Basal epithelial cells of the JE and of adjacent sulcular epithelium also have intense p75-NGFR-IR. In the present study we removed a wedge of the free ging iva and JE from the anterior side of the maxillary first molar of adul t rats, and then studied the return of nerve fibers during tissue rege neration from 1-63 days after gingivectomy. The nerve fibers entered t he adjacent healing sulcular epithelium before innervating the new JE, in both cases prior to return of epithelial cell p75-NGFR-IR. The reg enerating nerve fibers completely bypassed the zone of epithelial down -growth (long junctional epithelium, LJE) that was briefly present alo ng the tooth from 1-3 weeks after injury. The LJE did not have p75-NGF R-IR and was gradually replaced by a modified thicker regenerated junc tional epithelium (RJE). The RJE was attached along the injured root s urface, had numerous nerves in basal layers, and it had begun to regai n p75-NGFR-IR staining of basal epithelial cells by 22 d. Regenerating nerve fibers at 6-10 d had unusually weak CGRP-IR and greatly increas ed p75-NGFR-IR. Both nerve stains had returned to normal by 3-6 weeks. The intense p75-NGFR-IR of regenerating nerves was found on both axon al and Schwann cell membranes using electron microscopic immunocytoche mistry. In both the normal and regenerating JE, nerve fibers were rare in the attachment layers next to the anterior side of the maxillary f irst molar, compared to well-innervated basal layers. The complete avo idance of LJE by regenerating nerve fibers and its lack of p75-NGFR-IR suggest that its functions do not require innervation and that it doe s not make neurotrophic growth factors.